/Engine/Source/Runtime/Experimental/GeometryCollectionEngine/Public/GeometryCollection/GeometryCollectionISMPoolComponent.h
Adds a new mesh with instance count. We expect to only add a unique mesh instance once to each group. Returns a ID that can be used to update the instances.
[FMeshId](API\Runtime\GeometryCollectionEngine\GeometryCollection\FGeometryCollect-_13\FMeshId) AddMesh ( const [FGeometryCollectionStaticMeshInstance](API\Runtime\GeometryCollectionEngine\GeometryCollection\FGeometryCollect-_22) & MeshInstance, int32 InstanceCount, const [FGeometryCollectionMeshInfo](API\Runtime\GeometryCollectionEngine\GeometryCollection\FGeometryCollect-_14) & ISMInstanceInfo )